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12th Class Physics Magnetism Question Bank MCQ - Moving Charges and Magnetism

  • question_answer
    The final torque on a coil having magnetic moment \[25\text{ }A{{m}^{2}}\] in a 5 T uniform external magnetic field, if the coil rotates through an angle of \[60{}^\circ \] under the influence of the magnetic field is:

    A) 216.5 Nm                     

    B) 108.25 Nm

    C) 102.5 N m                    

    D) 258.1 N m

    Correct Answer: B

    Solution :

    (b) 108.25 Nm. \[|\overrightarrow{\tau }|=|\overrightarrow{M}\times \overrightarrow{B}|=mB\sin \theta \] Here,     \[M=25A\,{{m}^{2}};\theta =60{}^\circ ;B=5T\] \[\therefore \tau =25\times 5\times \sin \,60{}^\circ \] or           \[\tau =125\times \frac{\sqrt{3}}{2}108.25\,Nm.\]


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